In the past, conventional blinds for windows have typically been either venetian style blinds with transverse strips, or so called vertical blinds carried on individual trolleys on a horizontal track. These blinds could have a mechanism whereby the strips could be rotated between closed and open positions. However in the open position, in which light is transmitted into the room, there was also a loss of privacy. In the closed position, the light was obscured.
Other blinds are known which simply consist of a panel of thick flexible material, wound onto a roller. The material can be pulled down for privacy, and to obscure the light, or raised, to allow passage of light, but with loss of privacy.
Such basic roller blinds were relatively crude construction consisting simply of a roller with an interior spring, and a ratchet lock. There were also not particularly pleasing to the eye.
Recent developments in blind design have found that consumers are interested in obtaining blinds with a greater variety of light and shade effects, but which none the less provide for privacy preferably such blinds appealing to modern consumer tastes will have a more pleasing appearance, and be capable of fitting in with a variety of different interior design themes.
For this purpose, a window covering material may be provided, which is preferably somewhat translucent and is carried in the head rail. This covering material is light permeable, but provides privacy.
A second blind panel is stored in the head rail and is formed of opaque material. When complete light exclusion is required this second panel can be lowered.
In the first place the head rail must be compact and aesthetically pleasing. Desirably the blind head rail shall occupy no more space, or only slightly more space at the top of the window opening than previously known blinds.
The operation of the separate blind panels must be simple and capable of being operated by either manual controls, or in the case of more complex designs by means of power controls, and even remotely operated power controls.
One problem is experienced with such controls, is that some space must be allowed for the cord loops to hang beside one edge of the blind panels.
This space along one vertical edge of the blind panels, then allows some light in, and the blind fails to obscure all light.
Another problem is that when an operator manipulates the cords, the edges of the panels gradually become damaged. The appearance, and life, of the blind is therefor impaired.